1. Field of the Invention
This invention is directed to a control system for an electrostatic dust collection system. In particular, this invention relates to electrostatic dust collection control systems having means for adjusting system parameters responsive to feedback signals from the system. More in particular, this invention relates to an electrostatic dust collection control system which periodically determines what operating system parameters produce back corona conditions and then automatically adjusts the system operating parameters to substantially preclude generation of back corona. Still further, this invention directs itself to an electrostatic dust collection control system which utilizes multiple methods for detecting the existence of a back corona condition. Further, this invention relates to an electrostatic dust precipitator control system which automatically periodically determines what operating conditions are conducive to back corona generation and uses those values to limit the input power supplied to the high voltage transformer/rectifier of the system to substantially prevent back corona in the precipitator. Additionally, the control system provides for optimization of an intermittent mode of operation wherein the number of "off" cycles between energizing "on" cycles is optimized to prevent back corona.
2. Prior Art
Control systems for electrostatic dust collection systems are well known in the art. The best prior art known to the Applicants include U.S. Pat. No. 4,811,197; U.S. Pat. No. 4,390,830; U.S. Pat. No. 4,521,228; U.S. Pat. No. 4,432,061; and, U.S. Pat. No. 4,326,860.
In some prior art systems, such as that disclosed in U.S. Pat. No. 4,811,197, having the same Assignee as the instant invention, an adaptive control system is utilized for controlling the operating parameters of the dust precipitator responsive to feedback signals from the high voltage transformer/rectifier supplying the precipitator. However, that system utilizes only a single method for determining the existence of back corona, utilizing a decrease in slope of the minimum AC ripple waveform to identify the existence of back corona. While this method is a better method of detection than use of the average value of the secondary voltage, it is not as accurate in determining the existence of back corona as the method of monitoring the instantaneous minimum voltage peak value, as utilized in the instant invention. Further, to insure detection of the existence of back corona, the instant invention, utilizes two methods for analyzing the secondary voltage applied to the precipitator, which provides a more accurate indication of back corona conditions, not seen in the prior art.
In other prior art systems, such as that disclosed in U.S. Pat. No. 4,390,830, there is provided a control system which identifies back corona by comparing the current supplied to the precipitator with an average value of the precipitator voltage, to indicate the presence of back corona when the current begins to increase more rapidly than the voltage. The control system responds to back corona detection by reducing the current until the back corona condition is minimized in an attempt to operate at the knee of the voltage/current curve. However, the voltage/current curve characteristic exhibits a hysteresis type effect when the current is just lowered, as opposed to being removed totally and the system then driven to the desired lower current value, and thus such prior art systems do not maximize the operating voltage of the precipitator, as provided by the instant invention.